Magnetic speedometer.



J. K. STEWART. MAGNETIC sPEEDDMF-TER. APPLICATION FILED AUG.18, 1911.

- Patented Mar. 4,1913.

U11 TED. STATES ATENT oFFIo JOHN K. s 'rewaer, or cmcao, ILLINOIS,ASSIGNOR T STEWART-WARNER SPEEDQMETER conrona'rron, or THE STATE orVIRGI'NIA.

' meantime summar se.

p me r n s men Patented Mar .4,1913.

'Applica-tiolt filed August 18', 1911. Serial no, 644,732.

T 0 all whom it may concern:

' Be it known that I, JOHN STEWART, a

, citizen of the United States, residingat Chicagofin the county of Cookand State of Illinois. have invented new and useful Improvements inMagnetic Speedom'eters,

of which the following is a specification, reference being had to theaccompanying drawings, forming a part thereof.

The purpose of this invention is to pro- 'vide in combination with amagnetic speedometer. means for automatically adjusting theparts-thereof "to compensate the errors of indication otherwise changesof temperature.

introduced by It consists of the features and elements described andshown in the drawings as lindia cated in the claims.-

In drawings :Figure 1 is 'a' vertical section of a speedometer embodyingthis invention. Fig. 2 i's'a horizontal section of the same taken asindicated at line 2-2 on Fig. 1. Fig. -3 is a detail elevation of theelements, 4 and 14, hereinafter 'descrlbed. Fig.4 is an enlarged detailview'show-lng-the connection between the elements, 14 and 15.

magnets and thus to strengthen the mag netic field in their vicinity.The ring, 4, is spaced apart from the magnets by a short distance.leaving an annular space into which there protrudes the flange orvertical wall, of the non-magnetic element, 5, a

which is shown in the form of an inverted cup carried by a spindle, 6,and journaled in jewel bearings, 7, being biased toward a position ofrest by a' spring indicated at, 8. The driving shaft, 9, terminatlng ina m1ter gear, 10, which meshes with a gear, 11, on the carrier, '2, isdesigned-for operative connection with the rotating element whose speedis to be measured so that the-rotation of such element will causeacontinuous rotation of the carrier, 2, with the ma'gnets,

3, 3, upon it. According to a well understood law which need not here befurther explained, the rotation of the magnets, 3, 3,

produces what isknownas a magnetic drag,

which acts upon the non-magnetic element,v

5, tending to bias itaway from its position of rest. The amount by whichthe element, 5, is deflected from its position of rest beingproportional to the .speed of rotation of the magnets, 3,3, anindication-of speedis'obtained by fitting the spindle, 6, with an indeXneedle, 12, positioned to swing over a dial plate, 13, in the 'topiofthe case.

' As is well-understood', the effectiveness of the magnetic drag uponthe element, 5,

depends upon the electrical conductivity of the latter,- and since thiselectrical conductivlty is somewhat reduced by an appreci-- able rise oftemperature, the amount of defleet-ion of thecup, 5, and the needle, 12,will vary with changes of temperature and the indication of speed. willnot be a .true one unless .somemean's of compensating this error.isjemployed. The present invention consists inproviding the soft ironring-,4,

with a series of apertures, 4 in the vicinity of the poles of themagnets, 3, 3,}and mounting within the said ring, 4, a. second ring,14,. also of soft iron. This inner ring, 14, is provided with apertures,14 corresponding in spacing and dimensions to those of the ring, 4', sothat by slightly'rotating the ring, 14, within the ring, 4, theapertures of the latter may be partially or wholly closed,

and in this way a variable area of soft iron maybe presented to thelines of force of the magnetic field about the poles of the magnets, 3,3,-and the effectiveness of the soft iron rings in concentrating thisfield toward the. annularspace into which the cup, 5, is projected,maybe varied, and this variation of the strength of the magnetic fieldmay be employed to compensate for the c h: 1nge of effectiveness of thefield with change. of temperature. The movement of the ring, 14, withrespect to the ring, 4, is

arranged to be accomplished thermost'ati- 'cally by means of abi-metallic bar, 15 composed of two strips, 15 and 15 of differentmetals, respectively,and coiled within the soft iron rings in the shapeof, the "letter .C, with one end rigidly secured to the ring,

4, and the other end operatively connected tothe-ring, 14.. j Fig. 1illustrates a. rectangular yoke, 16, which is. riveted to, thebaseflange, 4 of the ring, 4, and is provided with a set screw, 17,which engages the end of the bar, 15; while the other end of the bar, asmay be understood from Figs. 2 and 4, is embraced betweena pair ofupstanding lugs, 14. on the base flange of the ring, 14, one of the lugsbeing accommodated in a vertical groove 15 in the side of the bar 15, soas to definitely engage it for moving it; It the metal, 15, on theinside of the curved ring, 15, has a high-er coeflicient of expansionthan the metal of the. strip, 15,, then with a rise of temperature thebar, 15, will tend to straighten out or reduce its curvature, withenough to compensate for the decrease of conductivity, which an increasein temperature occasions in the non-magnetic element, 5, and themagnetic drag operating between the said field and the element, 5, maybe kept practically constant throughout the range of temperatures towhich the instrument would ordinarily be subjected.

As may be seen from Fig. 2 each of the magnets, 3, is semi-annular orrather, just short of semi-annular in 'form and is mounted to rotateabout its own axis. This arrangement of the magnetic element has theadvantage of providing two pairs of poles, each pair being separated bya gap so that a field of force is created at two places symmetricallylocated with respect to the axis of revolution. This results in abetterbalanced torque with respect to the biasedelement, 5, than when asingle magnet in the form of a split ring is employed, and experienceseems to indicate that. an increase of efliciency is also obtained asa-resu'lt of the provision of twopairs of poles in place of the singlep..lr which exists in the split ring or C-form of magnet. I

It will be understood that'these advantages are not confined to the useof two magnets, as shown in the drawings, but that they might be presenteven to a greater degree if the annular magnetic element were dividedinto several segments, each separated from the adjacent segments at thepoles. Preferably, where two or more segments are employed, they arepositioned with unlike poles facing each other, since this arrange mentbest serves to prevent deterioration of their magnetic qualities. w

I claim I 1. In a 'magnetic speedometer, in combi nation with arevoluble magnet, an opposed magnetic mass or armature, an interposed 1element of low electrical resistance mounted for rotation. and means forbiasing .it against rotation in one direction, the magnetic mass beingcomposed of a member havin an a )erture )ositioned onosite the c: l l llmagnet poles and another member adapted toclose the aperture, saidarmature members being relatively movableto vary the extent of suchclosure of the aperture.

2. In a magnetic speedometer, in combination with a rotatable magneticfield, a biased element 'mounted for oscillation in .the field, and an.armature positioned for concent at-ing the field in the path ofoscillation of said biased element, said armature comprising two membersthe area of one of which is interrupted and the other positioned forspanning or covering such inter ruption, said armature members beingrelatively movable to vary the extentof the interruption remaininguncovered, and means for effecting such relative movement.

In a magnetic speedometer, in combination with a revoluble magnet, anopposed magneticmass or armature, an interposed element of lowelectrical resistance mounted for rotation, means for biasing saidelement against rotation in one direction, the magnetic mass beingcomposed of a member having an aperture positioned opposite the magnetpoles and another member adapted inostatic device operatively connectedwith the armature members relative movement.

for effecting their nation with a revoluble' magnet, an opposed-.magnetic mass or armature, an interposedelement of low electricalresistancemounted.

for rotation, means for biasing saidele'ment againstrotation in onedirect-1011, the magnetic mass being-composed-of a member having anaperture positioned opposite the magnet poles and another member adaptedto close the aperture, said armature members being relatively movable tovary the extent of such closure of the aperture, and a bi-metalliccurved bar having its ends connected, respectively, to the two armaturemembers for causing their relative movement with change of temperature.

5. In a magnetic speedometer, a magnet element mounted for rotation andcomprising a plurality of magnets, eacha segment of. an annulus, whoseaxisis the axis of rotation; a biased element'mounted for oscil'. lationin the field of said magnet element and an armature positioned forconcentrating said field in thepath of oscillation,

of said biased element.

'6. In a magnetic speedometer, a magnet clement mounted for rotation andcomprising a plurality of magnets, each a segment 1 3 7 theirrespectively opposite poles facing each" Augustff1911i.

v latiori in the field of themagnet element,

of an annulus fwhose axis'is the axis of 1-0 L In testimony wheneOfQ-Ihavehgrgmi set tation, such magnets being assembled with my hand-at(zfhicz'lgo, Il1'.,-t-h is"-1j1th day ef w bther; a biased elementmounted for osciI- H Km STEWART and an'armature positioned forc0nentrat-. Witnesses: ing said field in the paf'fibf usciliation of,CHAs. S. BURTON,

' the biased element. E'nNA M. MACINT QH.

